Aspects of parasexual analysis in Aspergillus parasiticus.

A scanning electron microscopic examination of the surface ornamentation of haploid, heterokaryotic, and diploid conidiospores of Aspergillus parasiticus is presented. Previous studies on the parasexual cycle in this aflatoxin-producing species have shown that heterozygous diploids may be isolated with ease. However, rational genetic analysis of diploids has been hampered by the nonrandom recovery of auxotrophic markers from heterozygous diploids. In this study, a double transfer method involving only brief exposure to p-fluorophenylalanine (FPA) allowed increased recovery of auxotrophic markers from heterozygous diploids. Extensive sampling of green-spored types from FPA-treated diploids provided an estimate of auxotrophic segregants not visually identifiable. We examined seven heterozygous diploids involving three spore color markers and eight auxotrophic markers. In addition, two mutants blocked in aflatoxin production which accumulated visually detectable aflatoxin precursors were analyzed. One linkage between an auxotrophic marker and a spore color marker was detected; however, no evidence for linkage was found between the blocked aflatoxin mutants and the other markers studied.